opt(v0.1.14): enhance syntax highlight — rAF throttle, regex order, large-doc skip

opt(core): _highlightEditor rAF throttle to avoid per-keystroke reflow
opt(core): fix regex order — image before link, code before bold, italic last
opt(core): skip highlighting for documents >50KB to prevent lag
opt(core): add toggleSyntaxHighlight() API method
fix(core): clear _hlRaf in destroy to prevent post-mortem callbacks
fix(core): initialize _hlRaf = null in constructor

src/core.js

@@ -115,6 +115,7 @@ class MarkdownEditor {
     this._zenMode = false;         // v0.1.12: Zen 模式
     this._wordWrap = true;         // v0.1.12: 自动换行
     this._syncing = false;         // 滚动同步锁
+    this._hlRaf = null;            // v0.1.14: 高亮节流
 
     // 渲染函数：自定义覆盖内置解析器
     this._renderFn = (typeof this.config.render === 'function') ? this.config.render : parseMarkdown;
@@ -1318,32 +1319,44 @@ class MarkdownEditor {
   // ============ 语法高亮编辑区（v0.1.14） ============
 
   _highlightEditor() {
-    if (!this.highlightLayer) return;
+    if (!this.highlightLayer || !this.config.syntaxHighlight) return;
+    // rAF 节流，避免高频更新
+    if (this._hlRaf) return;
+    this._hlRaf = requestAnimationFrame(() => {
+      this._hlRaf = null;
+      this._doHighlight();
+    });
+  }
+
+  _doHighlight() {
     const text = this._value || '';
     if (!text) { this.highlightLayer.innerHTML = ''; return; }
+    // 超过 50KB 跳过，避免大文档卡顿
+    if (text.length > 50000) { this.highlightLayer.innerHTML = escapeHTML(text) + '\n'; return; }
 
-    // 轻量级 tokenizer：正则匹配所有语法模式，包裹为 span
     let html = escapeHTML(text);
 
-    // 标题
-    html = html.replace(/^(#{1,6})\s+(.+)$/gm, '<span class="mh-heading">$&</span>');
-    // 粗体
-    html = html.replace(/(\*\*|__)(.+?)\1/g, '<span class="mh-bold">$&</span>');
-    // 斜体
-    html = html.replace(/(?<!\*)\*(?!\*)(.+?)\*(?!\*)/g, '<span class="mh-italic">$&</span>');
-    // 删除线
-    html = html.replace(/~~(.+?)~~/g, '<span class="mh-strike">$&</span>');
-    // 行内代码
-    html = html.replace(/`([^`]+)`/g, '<span class="mh-code">$&</span>');
-    // 链接
-    html = html.replace(/\[([^\]]+)\]\(([^)]+)\)/g, '<span class="mh-link">$&</span>');
-    // 图片
+    // 正则按优先级：先匹配更具体的模式，避免被泛模式吞掉
+    // 1. 图片（先于链接）
     html = html.replace(/!\[([^\]]*)\]\(([^)]+)\)/g, '<span class="mh-image">$&</span>');
-    // 列表标记
+    // 2. 链接
+    html = html.replace(/\[([^\]]+)\]\(([^)]+)\)/g, '<span class="mh-link">$&</span>');
+    // 3. 行内代码（先于粗体/斜体，避免 `**` 被误匹配）
+    html = html.replace(/`([^`]+)`/g, '<span class="mh-code">$&</span>');
+    // 4. 粗体 **text** / __text__
+    html = html.replace(/(\*\*|__)(.+?)\1/g, '<span class="mh-bold">$&</span>');
+    // 5. 删除线
+    html = html.replace(/~~(.+?)~~/g, '<span class="mh-strike">$&</span>');
+    // 6. 斜体 *text* / _text_（在粗体之后，避免 ** 被拆成两个斜体）
+    html = html.replace(/(?<!\*)\*(?!\*)([^*\n]+?)\*(?!\*)/g, '<span class="mh-italic">$&</span>');
+    html = html.replace(/(?<!_)_(?!_)([^_\n]+?)_(?!_)/g, '<span class="mh-italic">$&</span>');
+    // 7. 标题（行级）
+    html = html.replace(/^(#{1,6})\s+(.+)$/gm, '<span class="mh-heading">$&</span>');
+    // 8. 列表标记
     html = html.replace(/^(\s*[-*+]|\d+\.)\s/gm, '<span class="mh-list">$&</span>');
-    // 引用
+    // 9. 引用
     html = html.replace(/^(&gt;)\s?/gm, '<span class="mh-quote">$&</span>');
-    // 水平线
+    // 10. 水平线
     html = html.replace(/^([-*_]{3,})\s*$/gm, '<span class="mh-hr">$&</span>');
 
     this.highlightLayer.innerHTML = html + '\n';
@@ -1351,6 +1364,19 @@ class MarkdownEditor {
     if (this.textarea) this.highlightLayer.scrollTop = this.textarea.scrollTop;
   }
 
+  /** 切换语法高亮（v0.1.14） */
+  toggleSyntaxHighlight() {
+    this.config.syntaxHighlight = !this.config.syntaxHighlight;
+    if (this.textarea) {
+      this.textarea.classList.toggle('me-textarea-highlight', this.config.syntaxHighlight);
+    }
+    if (!this.config.syntaxHighlight && this.highlightLayer) {
+      this.highlightLayer.innerHTML = '';
+    }
+    if (this.config.syntaxHighlight) this._doHighlight();
+    return this;
+  }
+
   _updateWordCount() {
     if (!this.config.wordCount || !this.statusEl) return;
     const text = this._value || '';
@@ -1737,6 +1763,7 @@ class MarkdownEditor {
     if (this._renderRaf) cancelAnimationFrame(this._renderRaf);
     if (this._historyTimer) clearTimeout(this._historyTimer);
     if (this._outlineTimer) clearTimeout(this._outlineTimer);
+    if (this._hlRaf) cancelAnimationFrame(this._hlRaf);
 
     this._cleanups.forEach((fn) => { try { fn(); } catch (_) {} });
     this._cleanups = [];